Devices to adjust motor vehicle headlights are generally composed of at least one fixed swivel joint solidary with a fixed support part, such as an intermediary mechanism plate or a collet, engaging in a concave seating of an attachment and hinging component, called the capsule, mounted on the element to be adjusted. An adjustment screw, screwing into the fixed support part, is endowed at one of its ends with a swivel joint engaging in a second concave seating of a second capsule, mounted on the element to be adjusted. Said adjustment is effected by manipulating the adjustment screw, which causes the component to be adjusted to pivot around its point(s) of attachment composed of the fixed swivel joint(s).
When the headlight is being adjusted, any point on the mobile part of the headlight defines a circle arc around its rotation axis, which, in the case of a device to adjust the height of the light beam, is broken down into a horizontal component along the axis of the adjustment screw, and a vertical component which is offset only by the deformation of various parts of the headlight and the adjustment device. This problem can cause elastic or permanent deformation of said parts, or the rupture thereof, and, in any case, increases the torque of the adjustment screw.